1. Field of the Invention
The present invention relates to a polymerization catalyst and a method for producing a polyolefin or an olefin block copolymer using the same. More particularly, the present invention relates to a method for producing a polyolefin or an olefin block copolymer by using an organic rare earth metal compound system catalyst having a high activity and an activity of long duration, which is usable for producing a high molecular polymer even at a high temperature. The present invention further relates to a novel olefin block copolymer obtained by block-polymerizing an olefin with an unsaturated carboxylic acid ester (hereinafter referred to as "unsaturated carboxylate"), and more particularly, the present invention relates to a novel olefin block copolymer obtained by block-polymerizing an olefin polymer block with a (meth)acrylate polymer block having a highly isotactic structure.
2. Discussion of Background
Heretofore, a Ziegler system catalyst has been widely used as a polymerization catalyst for olefins. However, when an olefin is subjected to copolymerization with a monomer having a polar group in the presence of a Ziegler system catalyst, the Ziegler system catalyst is highly reactive with a compound having a polar group and the catalyst is deactivated so that the copolymerization can not be satisfactorily conducted.
Recently, an organic rare earth metal compound system catalyst has been proposed as a uniform system catalyst for olefin polymerization. Particularly, it is reported that a catalyst having a cyclopentadiene derivative as a ligand has a high activity for polymerization of olefin, and that this catalyst or a combination of this catalyst with an organic aluminum compound can be applied to copolymerization of a monomer having a polar group (see Japanese Unexamined Patent Publications No. 255116/1991 and No. 53813/1992), but these catalysts have disadvantages that their catalytic activity and duration of activity are not satisfactory and that they are inconvenient to handle.
For example, U.S. Pat. No. 4,668,773 discloses an organic lanthanide compound of the formula Cp.sub.2 'MR (wherein Cp.sub.2 ' is [.eta..sup.5 -(CH.sub.3).sub.5 C.sub.5 ].sub.2, M is a lanthanide element, and R is a bistrimethylsilylmethyl group or the like), and its hydrogenated hydride compound (Cp.sub.2 'MH).sub.2, and also discloses that these compounds, particularly hydride system compounds are useful as an ultra-highly active catalyst for a uniform system olefin polymerization. However, this catalyst must be prepared immediately before using in polymerization since this catalyst is very unstable and is hard to be preserved even in a strict nitrogen atmosphere. Moreover, the activity maintenance of this catalyst is low, and many steps are required for preparing this catalyst. Also, this catalyst is expensive since it is hard to synthesize a silyl group-substituted alkyl group which is a starting material for preparing this catalyst.
Recently, the catalyst system consisting of a compound of Cp.sub.n MX.sub.4-n M'L.sub.x (wherein Cp is cyclopentadienyl or cyclopentadienyl substituted with an alkyl or alkylsilyl radical, M is a metal having an atomic number in the range of 58 to 71, M' is an alkali metal, L is a suitable electron donor ligand, X is a halogen, n is 1 or 2, and x is a number in the range of 1 to 3) and an alkyl metal such as BuLi and R.sub.2 Mg has been disclosed in U.S. Pat. No. 5,109,085, but the above U.S. patent does not mention the polymerization of alkyl(meth)acrylate at all. The catalyst system of this prior art can not provide a satisfactory isotactic polymer.
Moreover, it has been reported that the lanthanide metal complexes having alkylcyclopentadienyl ligands afford rather syndiotactic polymethylmethacrylate in homopolymerization and copolymerization with ethylene (for example, H. Yasuda et al, Macromolecules, 25, 5115 (1992)).
The present inventors have studied and found a novel polymerization catalyst comprising a reaction product of an organic rare earth metal compound of specific structure with a Grignard reagent, which does not have the above-mentioned disadvantages of the conventional catalysts. The catalyst of the present invention has a high catalytic activity, an activity of long duration and an ability to cause living polymerization to olefins and polar monomers, and is suitable for polymerizing or copolymerizing olefins. Also, a block copolymer of olefin can be satisfactorily prepared by introducing a polar monomer such as a (meth)acrylate monomer in the presence of the catalyst of the present invention after conducting polymerization of olefin for a predetermined time, and it has been found that the olefin(meth)acrylate block copolymer thus obtained is a novel block copolymer having a highly isotactic structure as compared with the conventionally known olefin(meth)acrylate block copolymer.
The catalyst system of the above cited U.S. Pat. No. 5,109,085 is essentially different from the catalyst system of the present invention since the former catalyst employs an alkyl lithium or a dialkyl magnesium as a co-catalyst, whereas the latter catalyst employs an alkyl magnesium halide. The catalyst of this prior art can not provide a satisfactory isotactic copolymer, but rather provides a copolymer being rich in syndiotactic structure. On the other hand, the catalyst of the present invention can provide a satisfactory highly isotactic polymer which is the desired product of the present invention. As to the homopolymerization of ethylene, also, the catalyst of the present invention has the characteristic that it brings less transfer reaction at a high temperature (e.g. 70.degree.-80.degree. C.), thus providing a higher molecular weight, which is favorable for industrial use, whereas the catalyst of this prior art brings more transfer reaction at a high temperature and provides a lower molecular weight.